The Long Term Evolution (LTE) system adopts the physical layer frame on the basis of Orthogonal Frequency Division Multiplexing (OFDM) and Multiple-Input Multiple-Out-put (MIMO) technologies. In order to adapt to transmission environment better, the LTE system adopts various kinds of adaptive technologies. Based on different application scenes, 8 kinds of downlink transmission modes are defined in the LTE Rel-8/9 system, while another new kind of transmission mode needs to be defined in the Rel-10 system to support top 8 layers' downlink MIMO transmission. Based on the adapting foundation of transmission mode, the evolved Node B (eNB) in Transmission Mode (TM) 4, 7, 8 and 9 is able to select downlink transmission rank adaptively according to spatial characteristics of channels. Theoretically speaking, the network side is able to adjust data rate of each data layer through controlling modulation order and code rate, so as to match transmission capability of each spatial data channel precisely. However, considering control complexity and feedback overhead, the MIMO transmission of LTE system can support dynamic adjustment of at most 2-codeword Modulation & Coding Scheme (MCS). Within the transmission bandwidth of the LTE system, channel response often shows obvious frequency selectivity, thus the eNB can select User Equipment (UE) and schedule flexibly according to the channel state and interference condition at each frequency band of each UE, so as to acquire frequency selective scheduling and multi-user diversity gain. In the mean time, the network side can allocate resources reasonably according to channel state at each frequency band to avoid interference among cells.
Channel quality information is the important foundation of all kinds of adaptive adjustments and scheduling performed by the network side. The LTE system quantizes channel quality into 4-bit Channel Quality Indicator (CQI), label of each CQI corresponds to an assembly of modulation mode and code rate, under which the UE should guarantee the error probability of receiving transmission block to be within 0.1.
When calculating CQI, the UE needs to assume the transmission scheme of the Physical Downlink Shared Channel (PDSCH) according to its transmission mode. For example, when calculating the CQI defined in the LTE Rel-9 system, assumption mode of the PDSCH transmission scheme is shown in Table 1.
TABLE 1Assumption of PDSCH TransmissionScheme When Calculating the CQITransmis-Transmission scheme ofsion modePDSCHDescription1Single-antenna port, port 0Single-antenna port, port 02Transmit diversityTransmit diversity3Transmit diversity if theTransmit diversity if theassociated rank indicatorassociated rank indicatoris 1, otherwise large delayis 1, otherwise large delayCDDCyclic Delay Diversity(CDD)4Closed-loop spatialClosed-loop spatialmultiplexingmultiplexing5Multi-user MIMOMulti-user MIMO6Closed-loop spatialClosed-loop spatialmultiplexing with a singlemultiplexing with a singletransmission layertransmission layer7If the number of PBCHIf the number of PBCHantenna ports is one,antenna ports is 1,Single-antenna port, port 0;single-antenna port, port 0;otherwise Transmit diversityotherwise transmit diversity8If the UE is configuredIf the UE is configuredwithout PMI/RI reporting:without PMI/RI reporting:if the number of PBCHif the number of PBCHantenna ports is one,antenna ports is 1,single-antenna port, port 0;single-antenna port, port 0;otherwise transmit diversityotherwise transmit diversityIf the UE is configured withIf the UE is configured withPMI/RI reporting: closed-PMI/RI reporting: closed-loop spatial multiplexingloop spatial multiplexing
The Cell-specific Reference Signal (CRS)-based measurement and demodulation mode are adopted in the transmission modes 1˜6 of the LTE Rel-8/9 system, while the CRS-based measurement and the Demodulation Reference Signal (DMRS)-based demodulation mechanism are adopted in TM 7 and TM 8; wherein, in TM 2˜6, the UE needs to calculate and report the recommended Precoding Matrix Indicator (PMI) according to measurement of the CRS; when reporting CQI, the UE assumes that the eNB uses the reported PMI. Non-codebook precoding mode is adopted in TM 7, the UE only needs to report the CQI to the eNB, then the eNB will calculate precoding or figurative vector. Both the PMI and non-PMI feedback modes are supported in the TM 9 system. Based on feedback mode of high-layer configuration and specific reporting mode, the UE can generate reporting content (including PMI/Rank Indication (RI)/CQI) according to the measurement of CRS. In the LTE Advanced (LTE-A) system, in order to support higher-order MIMO transmission (maximum supporting 8 data layers) and multi-cell combined treatment function in subsequent versions, a newly defined Channel State Information-Reference Signal (CSI-RS) is introduced. The UE working in TM 9 cannot generate CQI/PMI/RI reporting information without the measurement of CSI-RS.
In the procedure of realizing the present invention, at least the following problems exist in the current technologies:
In TM 9, for the transmission mode based PMI feedback, the UE can assume that the eNB uses the reported PMI/RI. On this basis, the UE can calculate the CQI of each codeword as per mode similar to closed-loop spatial multiplexing (such as TM 4 system). However, with regard to non-PMI feedback-based transmission mode, no CSI-RS based measurement or reporting method for channel quality information exists currently.